The present invention relates to an integral type lens in which two lenses, such as plastic lenses, are fitted to each other and are integrally combined with each other.
FIGS. 1 to 3 show a conventional integral type lens of this kind, FIG. 1 is an exploded perspective view of the lens. FIG. 2 is a cross-sectional view of the lens in the diametrical direction thereof. FIGS. 3A and 3B are views of two lenses seen from the inside thereof.
The integral type lens is used for a projecting lens of a projection television. In FIGS. 1 to 3, a first group of lenses 10 are disposed on the screen side of the projection television. Reference numeral 20 is a second group of lenses. The first group of lenses 10 and the second group of lenses 20 are constructed as spherical lenses as shown in FIG. 2 and are made of plastic for ease of processing.
Rim 10a is formed in the outer circumference of first lens group 10. Flange 20b is formed on side face 20a of second lens group 20. As shown in FIG. 2, when the first and second lens groups are integrally formed, these lens groups are fitted to each other such that side face 20a of second lens group 20 contacts an inside face of rim 10a of first lens group 10 and an upper face of flange 20b of second lens group 20 contacts a lower face of rim 10a.
When the above-mentioned plastic lenses are molded, a high degree of accuracy can be obtained in the face of the lens, but it is difficult to improve the accuracy of the lens diameter. Further, the size of a plastic lens molded by acrylate resin or the like is altered by changes in humidity temperature etc. Therefore, the inner diameter of rim 10a of the first lens group 10 is manufactured to be slightly greater than the outer diameter of side face 20a of the second lens group 20. When the first and second lens groups are fitted to each other, play therebetween is eliminated by disposing a member such as a tape, etc., in a clearance between contact faces of the first and second lens groups, and the thickness of the tape, etc., is adjusted to assemble the lens groups such that the optical axes of the respective lenses are in conformity with each other.
Therefore, in accordance with the conventional integral type lens mentioned above, it is difficult to accurately conform the optical axes of the two lens groups to each other and it takes a considerable amount of time to assemble the lens groups.